Vehicles, including automobiles, trucks, watercraft, and aircraft, have included electrical cabling for over a century. Electrical cabling has been in use on watercraft in particular since the early 1880s, when electric lights were first installed on the H.M.S. Inflexible. However, installation of these cables can be tedious and inefficient, due to the requirements of space, weight, and the amount of cabling required. For example, a modern airplane or ship may have more than a hundred miles of electrical wiring.
In the past, wiring has been installed in these vehicles using similar methods to those used in building construction: during the initial framing, while walls are still open, wires may be manually passed from one section to another and cut to length. After the walls are finished, the wires may be terminated in outlets and switches or other connectors. Accordingly, electricians are required to perform part of their work at one time, and part at another time, complicating project management and increasing expense. Unlike building construction, however, many land vehicles and aircraft are manufactured in mass assembly lines. The requirement of pausing assembly at a first stage to install electrical wiring and then returning at another stage to terminate wires reduces the efficiency gained in automation.
To reduce this inefficiency, manufacturers have taken advantage of the consistency of manufactured parts generated by assembly lines. Because the wires in every car of a specific model will be the same length and follow the same routing path, rather than pulling wires individually in the finished vehicle and cutting them to length, electricians can use worktables customized for the installation. For example, shown in FIG. 1A is a diagram of an embodiment of a wire harness 100 assembled on a wireboard 102. The wireboard may be plywood or other materials, and may include pins or nails 104 placed along a path. Wires 106 may be routed along the paths defined by these pins and cut to lengths specified on the wireboard 102. Connectors 108 may be installed on the wireboard, and the wires may be tied or bundled together to form the harness. Referring now to FIG. 1B, the preassembled wire harness 100 may be removed from the wireboard and installed into a vehicle, confident in the knowledge that each wire will be the proper length for the various bends and turns it needs to take to reach instrument panels, switches, or other components.
The same technique may be used in the construction of a wire harness for an aircraft. Referring now to FIG. 2A, shown is a diagram of an embodiment of an airplane wire harness 200 assembled on a wireboard 202. The wireboard 202 may be a many pieces of plywood or other materials placed together to form a full-size outline of the aircraft. In some instances, due to the size involved, wireboard 202 may not physically exist, but rather comprise a large open space, such as the floor of an airplane hangar or manufacturing plant and be painted or marked with an outline of the aircraft 203 or the locations of various components within the finished aircraft. In other embodiments, as shown in FIG. 1A, wires may be looped back on themselves to achieve the necessary length without requiring a full-size mockup. Similar to the creation of a wire harness shown in FIG. 1A, in FIG. 1B, wires 206 may be routed along pins 204 to final locations, cut to length, and terminated. The wires may then be tied or bundled to form a finished wire harness 200. Referring now to FIG. 2B, the preassembled wire harness 200 may be installed into premanufactured sections of the aircraft 210. Because the wire harness may be assembled separately from the vehicle, electricians can prepare multiple harnesses concurrently, increasing efficiency.
As shown in FIG. 2B, aircraft are manufactured in sections, which may then be joined together, simplifying installation. A wire harness stretching the full length of the aircraft can be run through openings between each section, and as the sections are brought together, may be attached to mounting points or connected to terminations such as engines, control surfaces, instrument panels, and other features. Vehicles are similarly constructed in sections that are joined together, such as doors bolted on to the main body. Accordingly, a wire harness may be fed through openings in the body and doors prior to attachment, and the openings may be of sufficient size to accommodate the large connectors required for multi-conductor cables.
Installation of cables into watercraft poses significant additional problems, however. Shown in FIG. 3 is a cutaway diagram of an embodiment of a watercraft 300. Unlike manufacture of aircraft and automobiles, watercraft are frequently constructed by laying watertight bulkheads 304 along a keel and affixing the hull 302 at one time. Because of the watertight sections, pre-terminated wire harnesses may not be able to be pulled through bulkhead openings.
Furthermore, while a large assembly line may output thousands of cars per day with identical wire run lengths, ships are frequently custom designed or customized from a base design. Accordingly, even two ships built in succession by the same manufacturer may have very different wiring requirements. In the modern industrial shipbuilding technique known as block construction, sections of a large watercraft are built separately before being bolted and welded together. Although similar to the sectioned construction of aircraft shown in FIG. 2B, the customization of watercraft means that prebuilt wire harnesses cannot be used even in these manufacturing techniques, because of imprecise calculations of wire run lengths. One answer would be to simply make every wire longer than necessary and leave the excess in loops at one end. However, this adds significant weight and takes up large amounts of room, particularly with the hundreds of miles of wiring in modern watercraft. Furthermore, because connectors used in watercraft are frequently large, particularly for military-grade or MIL-SPEC installations required on naval vessels or when a cable includes multiple conductors to be terminated in a multi-pin connector, the connectors may be too large to be preinstalled and pulled through watertight cable throughways, ductwork, and other pass-throughs in watertight bulkheads. Accordingly, cables are still installed in watercraft today in the same inefficient pull-cut-terminate method used over one hundred years ago.